AQA Combined Science (8464) 6.3.2.2 · Quantitative
Temperature changes and specific heat capacity
Heat two things with the same energy and one ends up far hotter. What decides how far a temperature rises, and how do you measure the property that decides it?
Combined Science · Foundation tier
Start here
Sand and sea, same sunshine.
On a sunny afternoon at the beach, the dry sand and the sea next to it get the same sunshine all day.
If you had to guess, if 1 kg of dry sand and 1 kg of seawater get exactly the same energy, which warms up more?
Heat a material and its temperature rises. How far it rises depends on three things: the mass being heated, the material, and the energy put in. The material’s part is its specific heat capacity, c: the energy needed to raise the temperature of 1 kg of the substance by 1 °C. Water’s is 4200 J/kg °C, one of the highest of any common substance. One equation links all three to the temperature change, Δθ.
Equations
ΔE = m c Δθ
change in thermal energy (J) = mass (kg) × specific heat capacity (J/kg °C) × temperature change (°C)
Δθ = ΔE ÷ (m c) · c = ΔE ÷ (m Δθ) · m = ΔE ÷ (c Δθ)
E = P t
energy transferred (J) = power (W) × time (s). How an electric heater’s energy is found.
P = E ÷ t · t = E ÷ P
Mass, material, energy
Rank the temperature rises.
Identical heaters give each sample the energy on its card. Water: c = 4200 J/kg °C. Aluminium: c = 900 J/kg °C. Tap the samples in order, biggest rise first.
- 1st
- 2nd
- 3rd
- 4th
Required practical 14 · the AQA method
Heat a block with a known energy. Measure its temperature rise.
- Measure the mass of the metal block on a balance.
- Put the heater and the thermometer in the block’s two holes, with a few drops of water in the thermometer hole for good contact. Wrap the block in insulation.
- Connect the heater to a low-voltage supply through a joulemeter, or with an ammeter and a voltmeter. Record the starting temperature.
- Switch on and start the stopclock. Record the temperature every minute for 10 minutes.
- Switch off. Record the energy supplied (the joulemeter reading, or E = V × I × t) and the highest temperature the block reaches.
- Work out Δθ, then c = ΔE ÷ (m × Δθ).
- Independent
- Time of heating, which sets the energy supplied.
- Dependent
- The temperature of the block.
- Control
- The block’s mass and material, the heater’s power, the insulation.
- Risks
- The heater and block get hot enough to burn: do not touch them, and let them cool on a heat-proof mat. Clamp the thermometer so it cannot roll off and break.
Run the practical
Measure c for aluminium. Call it first.
Commit first. The data-book value for aluminium is 900 J/kg °C. The value you measure will be…
Think again · before you substitute
“Just put the numbers from the question straight in.”
Spot the flaw
Identify500 g of water is heated from 20 °C to 60 °C. A student writes ΔE = 500 × 4200 × 60. What is wrong?
Command words in this lesson
- Define
- Give the exact meaning: for c, energy, 1 kg and 1 °C all appear.
- Calculate
- Write every line: convert, equation, substitute, rearrange, answer with its unit.
- Explain
- Link cause to effect: where the energy went, what that did to Δθ, what that did to c.
- Describe a method
- Equipment, what you measure and how, in order, and how you work out the result.
Key fact
ΔE = m c Δθ, with Δθ = final − initial. Specific heat capacity is the energy needed to raise the temperature of 1 kg by 1 °C.
Key note · AQA 6.3.2.2 (8464) · RP14
Temperature changes and specific heat capacity
- SHC (c): J per kg per °C.
- ΔE = mcΔθ.
- Water c = 4200 J/kg°C (highest common).
- Δθ = final − initial.
- Rearrange for any unknown.
- Required practical 14: electric heater method.
- High SHC of water → radiators, cooling systems, climate moderation.
Photograph this card. Tomorrow, cover it and say each line first.
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Stuck on Δθ, or on which units to convert?
The practical simulates a 1.00 kg aluminium block (data-book c = 900 J/kg °C) and a 48 W heater. A fixed share of the heater’s energy escapes to the surroundings, a larger share without lagging, and the heater takes a little time to warm up. Readings carry a small random scatter. In the ranking, every sample is heated evenly and loses no energy. Real sand and sea also differ in how they absorb sunlight, and the sea mixes and evaporates.